help my misfire

Reply

  #1  
Old 02-11-05, 01:03 PM
Member
Thread Starter
Join Date: Sep 2004
Posts: 238
help my misfire

The car a í97 Chevy, Lumina with 3.1L and 40,000 owned by me since 11-04 randomly misfires. Maybe once every three weeks, which means maybe 1 in 200 starts.

Here is what I have observed:
It is always happens on start-up, never while driving.
The car is always cooler than operating temp. It may have sat for 2 hours or 2 days.
The weather and ambient temp does not seem to matter.
Except for one time, which is detailed below, the problem has been resolved by waiting. This means I stopped the car and immediately restarted it, or I came back to it after several hours to take a look, and it was then running fine.

The cylinder affected and frequency of each is as follows:
#3: 60%
#4: 35%
#2: 5%

My repair attempt:
Only once did the problem persist. I had a # 4 that would not run after waiting, so I did the following:

1. I switched coils to see if the problem moved with the coil. It did not and the problem stayed.
2. I switched plugs and wires to see if the problem would move. The problem stopped, and I could not prove anything, so I stopped.
3. A few days latter I switched the wires back to their original positions, since they are numbered and I did not want to be confused in the future.

Additional observations/reflections:
I may have moved the #4 plug to #2, but I donít remember. The one time the problem happened after I switched plugs around about 3 weeks ago was on #2.

The one strange thing I noticed was that the ground electrode on the #4 plug had a tit on it just like the tit I get on the points on my VW. I have never seen that on a plug, but I have no knowledge of platinum plugs and the problem did not move with the plug, so I though it was nothing.

I am stumped. All the wires and plugs look good. I donít think there is a problem with the coils or module. I understand that the cylinders spark in pairs, so I would think the misfire would happen in pairs if spark were the problem.

I was set to move injectors around, but I have doubts about that, since the problem is random and infrequent.

How is misfire detected?

Any ideas?
 
Sponsored Links
  #2  
Old 02-11-05, 02:04 PM
Member
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
I would get the injectors cleaned or add a strong injector cleaner to the tank and I would do some type of top engine cleaning with the engine running.A solvent designed and metered through a vacuum hose.If there is no corrossion on any coil tower or black soot,rust etc and nothing visable on the plug end or porcelin you may either have a sticking or clogged injector or some type of buildup on the valve stems.Be warned just because the scan tool says it's 1 certain cylinder that may not be the case.Always check the companion cylinder for the affected coil.1/4-2/5-6/3.Also change the fuel filter and check the fuel pressure with a guage 35-40psi would be ok.
 
  #3  
Old 02-11-05, 02:45 PM
Member
Thread Starter
Join Date: Sep 2004
Posts: 238
davo

What type (brand) of in-tank injector cleaner do you recommend?
Do you also mean spray something like Gumout into a vacuum hose with the engine running?

I'll try it thanks.
 
  #4  
Old 02-11-05, 03:02 PM
Member
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
Try using the fuel system cleaner first with a tank of premium and change the fuel filter.I won't mention a specific brand but buy the strongest one they have and use it according to directions.The intake cleaner must be metered through a valve to prevent engine damage so try the other stuff first and we can go from there.
 
  #5  
Old 02-13-05, 06:13 PM
Member
Thread Starter
Join Date: Sep 2004
Posts: 238
davo

I put the stuff in the tank and will do it again for the next tank.
Also, I changed fuel filter.

Per my gage, I had 41 psi w/ KOEO and 38 psi w/ KOER and vacuum to regulator. The readings were the same before and after the filter change.

I'll keep you posted.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes